Maintain the same notebook / scratch pad for all cases that you do. Use the same book to record the feedback that you receive.

Note down all main points that the interviewer tells you in the same space where you made notes for your case. Write in another ink if you like.

Categorize feedback – both positive and negative into the main aspects of performance, which are:

Structuring

Logical and hypothesis building

Math and other analysis

Communication and attitude

Figure out which of the good things and bad things you are repeating over time - which areas need improvement and which ones are strengths?

Know what exactly you need to do in order to improve. For e.g. Math practice, structuring, learning how to make it MECE, etc.Once you have this figured out, make time to work on special exercises or readings to improve in those areas.

Track the number of times you are making mistake and observe if there are some underlying habits that are causing you to make the same mistake (for eg. speaking too fast). These are the most difficult ones to fix IMO and sometimes you can be too conscious especially if it's an integral part of your general behaviour.

Also keep track of the "overall feedback of the case". The first question a recruiter will answer when you leave the interviewer leaves the room is a simple "Yes/No". When you're doing cases - with friends or with experts here on PrepLounge - I would encourage you to seek an honest yes/no to the question "Would you send me to the next round?"

[Detailed feedback] Every interviewer will give you different feedback. It makes sense to ask every interviewer for specific feedback (better yet to let him/her know in advance, so they can focus on these points).

I plan to do this for every case in a different sheet. After 10-20 cases, it's good to take a day to review these notes and sharpen your skills.